The present invention generally relates to loudspeakers used for sound reinforcement, and more particularly relates to loudspeakers capable of focusing a large amount of acoustic energy into a relatively narrow beam of intelligible sound that can be propagated over long distances.
Long throw acoustical transmitting systems have been devised using parabolic dishes to focus the acoustic energy produced by a driving transducer positioned at the focal point of the parabolic dish. One such loudspeaker system is described in U.S. Pat. No. 5,821,470. This patent describes a system in which a parabolic dish reflects acoustic power produced by a high frequency horn loaded driver, and in which a low frequency driver is embedded in the center of the dish for extending the low end of the system's frequency range. Parabolic dish systems such as disclosed in U.S. Pat. No. 5,821,470 are capable of producing a relatively narrow beam of high acoustic power for long throw applications. However, they have a number of disadvantages.
First, the parabolic dishes and the mechanical structures required to support a driver at the dishes focal point create a relatively large and bulky apparatus. Consequently, this type of system is not well suited to applications where space is limited. Also, the dish's beam width, at any single frequency or range of frequencies, is essentially a function of the physical geometry (shape and size of parabolic reflector, and distance and shape of horn and transducer suspended in front of reflector, which generates the sound). Therefore once the geometry is selected for a given design it is not possible to alter the beam width. Not only is the beam width fixed with a parabolic reflector design, the axis of the beam remains perpendicular to the center of the parabolic reflector so redirecting the beam can only be accomplished by physically moving the parabolic dish.
Parabolic dish systems have yet other drawbacks. Obtaining a constant beam width over a wide range of frequencies with a parabolic dish is usually not possible. Lower frequencies will have wider beam widths than higher frequencies. Still further, the transducer and horn assembly suspended in front of the parabolic dish presents some interference with the sound reflected off the dish, both as an object in the path of sound and as a reflective surface back to the dish potentially causing echoes, so the transducer and horn must be kept relatively small, limiting the amount of power that can be generated by the transducer. Finally, if very high sound pressure level is desired from the dish, the compression and rarefaction becomes so great in the throat of the horn that distortion results as a vacuum is produced (194 dB SPL will normally produce a vacuum).
Other design approaches to achieve a narrow beam of acoustic energy over a wide range of frequencies for long throw applications, such as large horns or waveguides or multiple horns and transducers, also suffer from most of the limitations noted above and are similarly large and impractical to alter or redirect once set up.
The present invention overcomes the drawbacks and limitations of existing acoustic long throw systems (parabolic dish, and other horn and transducer cabinet arrangements) by providing an improved loudspeaker system that is relatively compact and that is capable of producing a high power beam of acoustic energy without the constraints imposed by conventional acoustic focusing structures such as parabolic dishes and horns, and that can be designed for fixed beam systems or systems that produce beams that can be electronically steered or altered without physically moving the loudspeaker or changing its physical features. The long throw loudspeaker system of the invention also is capable of producing a beam of acoustic energy where the beam width is relatively constant over the operating frequency range of the system.